Why would popularity win over a certain group deemed heretics when the belief of Jesus was "word of mouth"?

In which way should the heresy of Christianity not be considered just as much form of truth then Christians believing in Trinity? Everyone in the first century was re interpreting Peter's message. This is how Gnostics came up and other forms of re-visionaries such as Arius. These battles occurred prior to the Council of Nicea which legalized the "pre existence doctrine of Jesus". So was Christianity as a foundation supposed to occur. If not from popularity?